U.S. patent number 6,623,975 [Application Number 09/851,192] was granted by the patent office on 2003-09-23 for method and system for vehicle emission testing.
This patent grant is currently assigned to Gordon-Darby Systems, Inc.. Invention is credited to S. Jay Gordon, Clifton Mahaffey, Robert J. Tefft.
United States Patent |
6,623,975 |
Tefft , et al. |
September 23, 2003 |
Method and system for vehicle emission testing
Abstract
A method and system for vehicle emission testing measures
pollutant concentration, but then provides for conversion of the
measured pollutant concentration into its corresponding pollutant
mass, thereby allowing for the calculation of a vehicle's emission
test scores for one or more common pollutants in units of mass per
distance. Through the use of the method and system of the present
invention, significantly more accurate results can be obtained as
compared to prior art test methods, and without the implementation,
operating, and maintenance costs of comparable test methods.
Inventors: |
Tefft; Robert J. (Crestwood,
KY), Gordon; S. Jay (Louisville, KY), Mahaffey;
Clifton (Louisville, KY) |
Assignee: |
Gordon-Darby Systems, Inc.
(Louisville, KY)
|
Family
ID: |
28044475 |
Appl.
No.: |
09/851,192 |
Filed: |
May 8, 2001 |
Current U.S.
Class: |
436/137; 436/127;
73/114.69; 73/114.71 |
Current CPC
Class: |
G01M
15/102 (20130101); Y10T 436/208339 (20150115); Y10T
436/20 (20150115) |
Current International
Class: |
G01M
15/10 (20060101); G01M 15/04 (20060101); G01N
033/22 (); G01N 033/00 (); G01L 003/26 () |
Field of
Search: |
;436/137,127
;73/23.31,116 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Warden; Jill
Assistant Examiner: Sines; Brian
Attorney, Agent or Firm: Stites & Harbison, PLLC Nagle,
Jr.; David W.
Parent Case Text
This application claims priority from U.S. provisional application
No. 60/202,958 filed May 9, 2000. This application relates to a
method and system for vehicle emission testing. The entire
disclosure contained in U.S. provisional application No. 60/202,958
is incorporated herein by this reference.
Claims
What is claimed is:
1. A method for determining the mass of a pollutant in an emissions
sample obtained form a particular vehicle to ascertain whether such
pollutant mass exceeds a defined standard, comprising the steps of:
extracting the emissions sample from the particular vehicle as it
is operated over a testing period comprised of a plurality of
discrete time intervals; deriving a standard exhaust flow factor
from a reference data set at each discrete time interval for the
particular vehicle based on certain vehicle attributes; analyzing
the emissions sample extracted from the particular vehicle to
measure the concentration of the pollutant in said sample at each
discrete time interval; and determining the mass of the pollutant
at each discrete time interval by multiplying the standard exhaust
flow factor by the measured concentration of the pollutant by the
known density of the pollutant.
2. A method as recited in claim 1, and further comprising the steps
of: plotting the mass of the pollutant over the testing period to
generate an emission profile; and integrating the emission profile
over the testing period to determine the total mass of the
pollutant.
3. A method as recited in claim 2, and further comprising the steps
of: dividing the total mass of the pollutant by the distance
traveled over the testing period to calculate a test score for the
pollutant; and comparing said test score against a defined
standard, wherein a test score exceeding the defined standard is
considered a failure.
4. A method as recited in claim 1, in which the derivation of the
standard exhaust flow factor comprises the following sub-steps:
characterizing the reference data set, which is comprised of a
plurality of actual emission testing records based on the certain
vehicle attributes, placing each testing record into at least one
reference data subset defined by pre-selected vehicle attributes;
selecting a reference data subset based on the vehicle attributes
of the particular vehicle from which the emissions sample is
extracted; determining a dilution factor and a diluted pollutant
concentration for each data point in the reference data subset,
each said data point corresponding with a discrete time interval of
the testing period for the particular vehicle from which the
emissions sample is extracted; determining a raw pollutant
concentration for each data point in the reference data subset by
multiplying the dilution factor by the diluted pollutant
concentration; and determining the standard exhaust flow factor for
the pollutant for each data point in the reference data subset,
which is a function of the raw pollutant concentration, a standard
density factor, and the actual measured mass of the pollutant as
provided through the reference data set.
5. A method as recited in claim 1, in which the extraction and
analysis of the emissions sample from the particular vehicle is
accomplished by: a narrow sample probe for insertion into the
tailpipe of the particular vehicle; a sampling line operably
connected to said sample probe; and an analyzer for detection of
the pollutant associated with and in gaseous communication with a
sample and calibration gas control system, said control system
being operably connected to the sampling line.
6. A method as recited in claim 1, in which the certain vehicle
attributes are selected from a group that includes: make, model,
year, manufacturer, inertia weight, and engine displacement.
Description
BACKGROUND OF THE INVENTION
Vehicle emissions have long been identified as a major contributor
to air pollution. As such, in geographical areas having
particularly poor air quality, the United States federal
government, through the Environmental Protection agency ("EPA"),
has mandated vehicle emission inspection and maintenance programs.
The intent or objective of these vehicle emission inspection and
maintenance programs is to identify vehicles which are no longer
performing acceptably, i.e., vehicles which are releasing more
polluting emissions than is acceptable. Vehicles identified as not
performing acceptably must then be appropriately repaired.
In implementing vehicle emission inspection and maintenance
programs, various apparatus, methods, and testing protocols have
been developed and are being used across the United States. In this
regard, the local municipality or similar governing body normally
makes the decision as to which apparatus, method, and/or protocol
to employ. For example, some municipalities have opted for
centralized testing locations, others have opted for decentralized
testing locations, and still others have opted for a hybrid
centralized/decentralized systems. In most cases, the ultimate
decision as to which apparatus, method, and/or protocol to employ
depends on a combination of factors, including, for example:
practicality, costs, and input from interested third parties. Thus,
there are often wide variations between the apparatus, methods,
and/or protocols employed in different geographic areas. Such
variations often result in differences in the reliability and
accuracy of the testing, along with differences in the amount of
labor and skill required to conduct the testing and to maintain the
equipment associated with that testing.
A few of the simpler vehicle emission test methods are: (1) the
Idle Mode Test, which measures emissions from an idling vehicle;
and (2) the Loaded Mode Test, which measures emissions from
vehicles driven at a constant speed. Although these two tests
provide general baseline information regarding vehicle emissions,
they are not representative of "real world" driving. As a result,
both the Idle Mode Test and the Loaded Mode Test often tend to
produce false positives. In other words, a vehicle might pass the
Idle Mode Test or Loaded Mode Test even though that vehicle is not
in compliance with federal guidelines. Quite clearly, such testing
failures are potentially detrimental to the air quality of a
geographic area because vehicles which require repair are not
appropriately identified, thus allowing for excessive release of
polluting emissions.
To address these problems, more rigorous test methods and protocols
have been developed, including the Acceleration Simulation Mode
(ASM) concentration test and Transient Mass Emission Inspections
(TMEI). Such test methods are clearly preferred as compared to the
Idle Mode Test and the Loaded Mode Test; however, along with
improved performance comes increased costs.
First, the ASM concentration test can be used in both centralized
and decentralized testing programs. In an ASM concentration test,
vehicles are driven at a fixed speed under a heavy load.
Nevertheless, because the vehicles are artificially loaded, false
failures can result. In other words, a vehicle might fail the ASM
concentration test even though that vehicle is in compliance with
federal guidelines. Although false failures are not detrimental to
the air quality of a geographic area, a false failure can be costly
to the vehicle owner who must have the vehicle examined at a repair
or maintenance facility, and then must have the vehicle re-tested.
Furthermore, a high percentage of false failures tends to result in
public distrust of vehicle emission testing.
Among the most advanced and accurate test methods are Transient
Mass Emission Inspections (TMEI), such as the IM240 and IM147. In
TMEI, a vehicle is tested at a variety of velocities,
accelerations, and decelerations. These velocities, accelerations,
and decelerations (collectively referred to as a "drive trace") are
representative of "real world" driving conditions and engine loads.
For example, an IM240 test includes a series of accelerations,
decelerations and speeds ranging from zero miles per hour (MPH) to
fifty-six MPH over a 240-second testing period. For the duration of
the testing period, emissions, including hydrocarbons (HC), carbon
monoxide (CO), carbon dioxide (CO.sub.2), and the oxides of
nitrogen (NO.sub.x), are individually accumulated over the drive
trace and normalized for the distance traveled. This recorded mass
per distance, normally reported as grams per mile (GPM), is then
reported as the vehicle's test score. The vehicle's test score for
each accumulated pollutant is compared to a federally defined
standard for that vehicle and that particular pollutant. A score
exceeding the defined standard is considered a failure.
Thus, since pollutant mass is measured in TMEI, as opposed to
pollutant concentration (Idle Mode, Loaded Mode and ASM testing), a
more accurate determination of the vehicle emission characteristics
can be generated. Nevertheless, TMEI have some shortcomings.
Conventional TMEI do not lend themselves well to decentralized
testing. Furthermore, they are inherently complex and costly to
implement, operate, and maintain.
It is therefore a paramount object of the present invention to
provide a method and system for vehicle emission testing that
relies on transient test drive traces with "real world" velocities,
accelerations, decelerations, and loading, a method and system that
provides a measurement of pollutant mass rather than pollutant
concentration, yet has relatively low implementation, operating,
and maintenance costs.
This and other objects and advantages of the present invention will
become apparent upon a reading of the following description.
SUMMARY OF THE INVENTION
This present invention pertains to a method and system for vehicle
emission testing. The method and system of the present invention
relies on transient test drive traces with "real world" velocities,
accelerations, decelerations and loading. More importantly,
however, although the method and system of the present invention
measures pollutant concentration, it provides for conversion of the
measured pollutant concentration into its corresponding pollutant
mass, thereby allowing for the calculation of a vehicle's emission
test scores for one or more common pollutants in units of mass per
distance. Through the use of the method and system of the present
invention, significantly more accurate results can be obtained as
compared to prior art test methods, and without the implementation,
operating, and maintenance costs of comparable test methods.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the equipment involved in typical
prior art Transient Mass Emission Inspections ("TMEI");
FIG. 1a is an enlarged view of the fitting of an emissions
collection vent with a conical inlet port over the tailpipe of the
vehicle to be tested in typical prior art Transient Mass Emission
Inspections ("TMEI");
FIG. 2 is a schematic view of the equipment involved in the method
and system of the present invention;
FIG. 2a is an enlarged view of the insertion of a sampling probe
into the tailpipe of the vehicle to be tested in the method and
system of the present invention; and
FIG. 3 is a flow chart depicting the steps involved in vehicle
emission testing in accordance with the method and system of the
present invention.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
The present invention is a method and system for vehicle emission
testing that relies on transient test drive traces with "real
world" velocities, accelerations, decelerations and loading, a
method and system that converts measured pollutant concentration
into its corresponding pollutant mass at relatively low
implementation, operating, and maintenance costs. Specifically, the
method and system of the present invention allows for the
calculation of a vehicle's emission test scores for one or more
common pollutants in units of mass per distance for subsequent
comparison of each such test score to a standard to determine if
the vehicle has passed or failed the emissions test. Through the
use of the method and system of the present invention,
significantly more accurate results can be obtained as compared to
Idle Mode, Loaded Mode, and ASM testing, but without the
implementation, operating, and maintenance costs of TMEI.
In implementing the method and system of the present invention, it
is necessary to obtain and use a reference data set. Specifically,
the method and system of the present invention relies upon
characteristic exhaust flow factors that are specific to selected
attributes of the vehicle being tested (including, but not limited
to make, model, and/or year), thus allowing for a measurement of
pollutant concentration to be computationally converted to a
measurement of pollutant mass. However, calculation of the
requisite characteristic flow factors requires reliance on a
reference data set.
In the preferred embodiment of the present invention as described
herein, the requisite reference data set was compiled through the
TMEI program in Maricopa County, Ariz. Specifically, the reference
data set is comprised of a random, representative sample of the
actual emissions testing records from the TMEI program in Maricopa
County, Arizona. Each record in the reference data set identifies
the tested vehicle by make, model, year, manufacturer, inertia
weight, and engine displacement. Each record further provides the
constant volume sampling (CVS) flow and drive trace associated with
the test, as will be further described below, along with the actual
results of the test--the measured pollutant masses for the tested
vehicle for each second of the drive trace.
This particular reference data set was selected because the
Maricopa County TMEI program is widely recognized within the
industry for the accuracy and consistency of its testing, and thus
often serves as a standard against which other vehicle emissions
tests are compared. Nevertheless, the use of this particular data
set is not intended to be limiting, but for illustrative purposes
only. Other reference data sets may be also be used in accordance
with the present invention without departing from the spirit and
scope of the present invention.
As mentioned above, the Maricopa County TMEI program is widely
recognized within the industry for the accuracy and consistency of
its testing. Referring now to FIGS. 1 and 1a, the equipment
involved in testing in the Maricopa County TMEI program includes:
(1) a dynamometer and associated controller 10 operably connected
to a computer 12 or similar microprocessor which is programmed to
generate a drive trace that replicates "real world" velocities,
accelerations, decelerations, and loading; (2) a constant volume
sampling (CVS) system generally comprised of an emissions
collection vent 14 with a conical inlet port 16 and a high-pressure
blower 18; and (3) a series of analyzers 20 for detection of
various pollutants or other emissions, e.g., HC, CO, CO.sub.2, and
NO.sub.x, said analyzers 20 being in gaseous communication with a
sample and calibration gas control system 21, which in turn is
operably connected to the CVS system by one or more sampling lines
22. Of final note, the system may also include one or more sample
filters 23a, 23b. The primary filter 23a removes extraneous
materials, such as rust pieces, that are drawn into the collection
vent 14. The secondary filter 23b removes smaller extraneous
materials that were able to pass through the primary filter 23a. In
general, such filters are employed to extend the life of the
testing equipment and to ensure the accuracy of the testing
process.
In this prior art test method and system, since the conical inlet
port 16 of the collection vent 14 fits around the tailpipe 8b of
the vehicle 8 being tested, the extracted tailpipe emissions sample
includes essentially all of the vehicle's tailpipe emissions. The
blower 18 also introduces some ambient air into the sample,
turbulently homogenizing the mixture of raw emissions and ambient
air so that the ambient air dilutes the tailpipe emissions. A small
portion of this homogenized mixture of raw emissions and ambient
air is then siphoned off through one or more sampling lines 22 and
introduced into the series of analyzers 20 for detection of various
pollutants or other emissions, e.g., HC, CO, CO.sub.2, and
NO.sub.x, each analyzer essentially generating an emission profile
for a specific type of pollutant.
The analyzers 20 are calibrated to detect pollutant concentration
in terms of: ##EQU1##
However, since the raw emissions are mixed and homogenized with
ambient air to generate a constant volume referred to as a "sample
volume," and the densities (mass per sample volume) of the
pollutants are known values, the output from the analyzers can be
calculated in terms of mass for each second of the drive trace,
specifically: ##EQU2##
If necessary, this calculation can be further refined to take into
account environmental factors, such as the humidity.
By plotting the calculated mass at each second of the drive trace,
an emissions profile for each measured pollutant emerges. The total
mass then can be determined by integrating the emission profile
over the duration of the test.
Finally, from the drive trace, the number of miles "driven" over
the duration of the test is determined. For any particular
pollutant, the specific vehicle's test "score" is calculated by
dividing the total mass of the specific pollutant by the number of
miles "driven." Of course, the calculated test score for the
particular pollutant is compared to the defined standard for that
vehicle and that pollutant. A score exceeding the defined standard
is considered a failure.
The method and system of the present invention also allows for
measurement of pollutant mass instead of pollutant concentration,
but does not require the elaborate CVS system and associated
equipment described above and as used in Maricopa County TMEI
program.
Referring now to FIGS. 2 and 2a, the equipment involved in testing
in accordance with the present invention: (1) a dynamometer and
associated controller 30 operably connected to a computer 32 or
similar microprocessor which is programmed to generate a drive
trace that replicates "real world" velocities, accelerations,
decelerations, and loading; (2) a narrow sample probe 34 with an
associated sampling line 36; and (3) a series of analyzers 38 for
detection of various pollutants or other emissions, e.g., HC, CO,
CO.sub.2, and NO.sub.x, said analyzers 38 being in gaseous
communication with a sample and calibration gas control system 40,
which in turn is operably connected to the sampling line 36.
Of further note, this system preferably includes a primary filter
42 for removing extraneous materials, such as rust pieces, that are
drawn into the sampling line 36. Subsequent to passing through the
primary filter 42, collected samples are passed through a
refrigerant dryer 44 which removes moisture from the collected
sample without adversely affecting pollutant measurements. It is
important to remove moisture in this manner to prevent condensation
as condensation in the sampling system can affect pollutant
measurement and also lead to system failure. Then, the collected
sample is passed through a secondary filter 46 which removes
smaller extraneous materials that were able to pass through the
primary filter 42.
In this regard, the testing equipment is very similar to that
commonly used in current Idle Mode, Loaded Mode and ASM test
methods. Unlike TMEI testing, the sample probe 34 is a narrow
instrument that is inserted deep into the tailpipe 8b of the
vehicle 8, rather than fitting over and around the tailpipe, and
thus draws samples that are not diluted by ambient air. The actual
measured values with respect to particular pollutants are therefore
measurements of pollutant concentration. Nevertheless, through
appropriate computational analysis, the measurement of pollutant
concentration can be converted to a measurement of pollutant mass,
as is described in detail below.
Referring now to FIG. 3, the method and system of the present
invention is summarized in flow chart form. First, as mentioned
above, calculation of the requisite characteristic exhaust flow
factors requires reliance on a reference data set, such as the
above-mentioned reference data set from the TMEI program in
Maricopa County, Ariz.--a data set compiled through IM240 testing.
Accordingly, the first step in the flow chart of FIG. 3 is the
extraction and characterization of the reference data set, as
indicated at block 100. In this regard, per-second drive trace test
data is extracted, and this data is characterized or keyed to
specific pre-selected vehicle attributes, such as: make, model,
year, manufacturer, inertia weight, and engine displacement. In
other words, test records are categorized and placed into reference
data subsets based on certain vehicle attributes. For example, a
reference data subset may include test records for all 1998 Honda
Accords having a four-cylinder engine. Of course, data could be
extracted in characterized in a number of ways based on various
combinations of vehicle attributes as desired by the user.
Next, dilution factors and diluted pollutant concentrations can be
determined for each data point (i.e., per second of the drive
trace) in a particular reference data subset, as indicated at block
102 of FIG. 3. Specifically, each record in the reference data
subset includes: the actual measured pollutant masses; the
background concentrations, i.e., the concentration of each
particular pollutant or other emission in ambient air; and the CVS
flow, the rate at which the homogenized mixture of emissions and
ambient air traverses the system as measured in cubic feet per
second. With such data, dilution factors and diluted pollutant
concentrations can be calculated by simultaneously solving the
following equation for all pollutants for each data point.
where ##EQU3##
Then, multiplying the dilution factors by the respective diluted
pollutant concentrations generates a raw pollutant concentration
for each data point in the reference data subset, as indicated at
block 104 of FIG. 3: ##EQU4##
With this information, and the pollutant mass data provided through
the reference data subset, it is then possible to calculate a raw
exhaust flow for each pollutant at each data point, as indicated at
block 106 of FIG. 3, as follows:
Raw Exhaust Flow=Actual Mass.sub.x /(Raw Concentration.sub.x
*DensF.sub.x) (5)
In practice, the actual raw exhaust flow will vary somewhat between
even essentially identical vehicles, i.e. those vehicles defined by
the same pre-selected attributes. Therefore, an optimum exhaust
flow or "Exhaust Flow Factor," an exhaust flow that best
characterizes the vehicles defined by specific attributes, must be
calculated for each second of the drive trace, as indicated at
block 108 of FIG. 3. Specifically, the optimum exhaust flow will be
the value at which error is minimized at any particular second. In
this regard, the "Predicted Mass.sub.x," the mass.sub.x for a
specified pollutant, is a product of the known raw concentration
and the unknown Exhaust Flow Factor: ##EQU5##
Since the Actual Mass.sub.x of each particular pollutant is known
from the reference data, the error at any second for any particular
pollutant can be determined as follows:
Substituting for Predicted Mass.sub.x :
Summing the error over all the pollutants and all members of the
data subset produces a single error value: ##EQU6##
Substituting for Error.sub.x for each pollutant and differentiating
with respect to the Exhaust Flow leads to Error.sub.N being at a
minimum when: ##EQU7##
where x=HC, CO, or NO.sub.x n=individual test record N=total number
of test records in data set
In short, through the derivation set forth in equations (6)-(10),
it becomes clear that the Exhaust Flow Factor, the exhaust flow
that best characterizes a vehicle defined by specific attributes,
is a function of the raw concentration and actual mass of each
pollutant at each second of the drive trace.
Once the Exhaust Flow Factor has been determined for vehicles
defined by the same pre-selected attributes for each second of the
drive trace, the concentration of a specific pollutant at any
second of the drive trace can be reported in terms of mass.
Specifically, as indicated at block 110 of FIG. 3, the measured
pollutant concentration data is obtained through testing as
described above with reference to FIG. 2 and 2A. As indicated at
block 112 of FIG. 3, the concentration data is converted to mass
data as follows: ##EQU8##
trace, an emissions profile for each measured pollutant emerges.
The total mass then can be determined by integrating the emission
profile over the duration of the test.
Finally, the number of miles "driven" over the duration of the test
is determined. For any particular pollutant, the specific vehicle's
test "score" is calculated by dividing the total mass of the
specific pollutant by the number of miles "driven." Of course, the
calculated test score for the particular pollutant is compared to
the defined standard for that vehicle and that pollutant. A score
exceeding the defined standard is considered a failure.
It is contemplated and preferred that all required computation is
accomplished through a digital computer program. With benefit of
the foregoing description, such programming is readily accomplished
by one of ordinary skill in the art using known programming
languages and techniques.
As a further refinement, it is contemplated that further
optimization of the conversion from pollutant concentration to
pollutant mass can be achieve by calculating pollutant-specific
multipliers that reduce, when possible, the number of false passes
and false failures to values below user-specified thresholds.
Therefore, through implementation of the method and system of the
present invention, pollutant mass, instead of pollutant
concentration, may be determined without the high implementation,
operating, and maintenance costs common to prior art testing
methods and systems.
It will be obvious to those skilled in the art that modifications
may be made to the preferred embodiments described herein without
departing from the spirit and scope of the present invention.
* * * * *